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Virtual Destructor in C++

The C++, when you have a class hierarchy with inheritance and you use polymorphism (i.e., you have base class pointers or references pointing to derived class objects), it’s a good practice to use a virtual destructor in the base class. A virtual destructor helps ensure that the destructor of the most derived class in the hierarchy is called when an object is deleted through a base class pointer or reference. This is essential for proper resource cleanup and preventing memory leaks.

Here’s how you declare and use a virtual destructor in C++:

C++
class Base {
public:
    Base() {
        // Constructor code
    }

    virtual ~Base() {
        // Virtual destructor code
    }
};

class Derived : public Base {
public:
    Derived() {
        // Derived class constructor code
    }

    ~Derived() {
        // Derived class destructor code
    }
};

int main() {
    Base* basePtr = new Derived;
    delete basePtr; // Calls the virtual destructor

    return 0;
}

In the code above:

  • The Base class has a virtual destructor declared with the virtual keyword.
  • The Derived class is derived from Base and also has a destructor.
  • In the main function, we create a Derived object using a Base pointer (Base* basePtr = new Derived;). Since the destructor in Base is declared as virtual, when we call delete basePtr, it correctly calls the destructor of the most derived class, which is Derived.

If you don’t use a virtual destructor in the base class, deleting an object through a base class pointer when the object is of a derived class type may lead to resource leaks because only the base class destructor would be called.

In summary, using a virtual destructor is essential in C++ when working with class hierarchies and polymorphism to ensure proper cleanup and prevent resource leaks when deleting objects through base class pointers or references.

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